The present invention relates to a vibration absorbing device provided between the machine body incorporating a vibration source and the handle in such portable machines as, for example concrete vibrators, chain saws, concrete breakers, rivet guns or belt sanders.
In the prior art are known vibrators which try to impart fluidity to raw or uncured concrete which had been poured into a mold so as to fill its corners by inserting a stick like vibrator into the concrete and transmitting vibration to the uncured concrete. There are two types of such vibrators known; one attaches an unbalanced weight to the shaft of a small size motor, houses the shaft in a sleeve casing, and revolves the eccentric shaft at a high speed; the other houses an unbalanced weighted shaft alone in the casing and a rotational movement from an outside source is transmitted to the said shaft via a hose housing a flexible shaft joined to the rear end of the casing.
The effective radius of these known types of concrete vibrators becomes bigger proportionate to the slump of concrete and to the accelerated speed of vibration. This accelerated vibration naturally varies in proportion to the second power of the speed of rotation of the shaft and in proportion to the amplitude of vibration. Thus, the effective range of vibration is said to increase validly in accordance with a higher speed of rotation. A generally used range is 7,000 - 10,000 rpm for the vibrational number and 1 - 3 mm for amplitude. Many of the type of concrete vibrators described above are small size, one-man operated portable machines with a total weight not exceeding 20 kg. Even a very large type machine would require only two operators and is portable. This type of vibrator has as a source of vibration either an electric motor incorporated within the machine body or an outside power source such as an internal combustion engine joined to the eccentrically load shaft encased in the main body via a flexible shaft. The vibrator is joined to an outside power source such as a portable generator or to an outside prime mover either with a cable for supplying the current or for controlling such a supply, or with a flexible hose through which is inserted the said flexible shaft. In other cases a hose coupling is attached directly to the machine body of the vibrator and joined to the said flexible hose. In both cases, the vibration of the machine body causes premature fatigue and damage to the portion where the hose coupling is joined to the flexible hose, and also exerts undesireable effects on the health of operators as they are directly subjected to the vibration.
In comparatively big sized concrete vibrators, the machine is so constructed that the machine body including the source of vibration has a support means attached thereto via yielding rubber, a hose coupling to connect the operating bar handle and the said flexible hose, and a cable for passing the current or a flexible shaft inserted through the said support means and the said yielding rubber and into the machine body. As has been mentioned above, the said yielding rubber directly receives the vibration from the machine body which results in an early fatigue and requires frequent replacement of the rubber. All of these disadvantageous effects bring about added costs and labor in maintenance.
Various difficulties explained above are encountered in machines other than concrete vibrators, i.e., rock drills, drills, rivet guns, chain saws, and lead to such occupational disease as chain saw disease. Although various vibration absorbing means to cut off vibration transmission to operators of these vibrator machines of the portable type have heretofore been proposed, there has not yet been proposed a means which sufficiently supports the weight of the machine and the reaction force during operation and at the same time effectively attenuates the vibration imparted to the operator.